Modelling CFC inventories and formation rates of Labrador Sea Water

A high-resolution model of the North Atlantic Ocean is used to examine the potential of chlorofluorocarbon (CFC) inventories for calculating the rate of Labrador Sea Water (LSW) formation. While the simulated CFC-11 inventory and its geographical distribution in 1997 is fairly similar to observations, the model indicates pronounced variations in the history of CFC uptake, reflecting pulsations in LSW renewal in response to changes in wintertime atmospheric conditions. The LSW formation rate based on the volume of newly homogenized water during a winter season varies between 0 Sv and 11 Sv, and it is correlated (with a lag of 1 year) with the North Atlantic Oscillation (NAO) Index. The CFC-based estimate of the mean LSW formation rate is 3.5–4.4 Sv, approximately representing the mean volumetric formation rate (4.3 Sv) for the period 1970–1997

Impact of an adiabatic correction technique on the simulation of CFC-12 in a model of the North Atlantic Ocean

A model of the North Atlantic Ocean is used to simulate the spreading of CFC‐12 from the Labrador Sea deep convection site. The standard version of the model fails to capture the local maximum in CFC‐12 concentration that is observed along the continental slope of the western boundary. Hydrographic data are used to apply a simple correction to the model's horizontal momentum equations. The corrected model is much more successful at capturing the nearslope maximum in CFC‐12 concentration than the uncorrected model and also exhibits a 50% increase of the deep southward export of CFC‐12 at 24°N. The difference between the two model runs is shown to be a consequence of the different paths taken by the Deep Western Boundary Current in the two model versions

Eddy-Permitting Ocean Circulation Hindcasts of Past Decades

International audienc

Regional Patterns of Sea Level Change Related to Interannual Variability and Multidecadal Trends in the Atlantic Meridional Overturning Circulation

Some studies of ocean climate model experiments suggest that regional changes in dynamic sea level could provide a valuable indicator of trends in the strength of the Atlantic meridional overturning circulation (MOC). This paper describes the use of a sequence of global ocean–ice model experiments to show that the diagnosed patterns of sea surface height (SSH) anomalies associated with changes in the MOC in the North Atlantic (NA) depend critically on the time scales of interest. Model hindcast simulations for 1958–2004 reproduce the observed pattern of SSH variability with extrema occurring along the Gulf Stream (GS) and in the subpolar gyre (SPG), but they also show that the pattern is primarily related to the wind-driven variability of MOC and gyre circulation on interannual time scales; it is reflected also in the leading EOF of SSH variability over the NA Ocean, as described in previous studies. The pattern, however, is not useful as a “fingerprint” of longer-term changes in the MOC: as shown with a companion experiment, a multidecadal, gradual decline in the MOC [of 5 Sv (1 Sv ≡ 106 m3 s−1) over 5 decades] induces a much broader, basin-scale SSH rise over the mid-to-high-latitude NA, with amplitudes of 20 cm. The detectability of such a trend is low along the GS since low-frequency SSH changes are effectively masked here by strong variability on shorter time scales. More favorable signal-to-noise ratios are found in the SPG and the eastern NA, where a MOC trend of 0.1 Sv yr−1 would leave a significant imprint in SSH already after about 20 years

Homologous Recombination Is Stimulated by a Decrease in dUTPase in Arabidopsis

Deoxyuridine triphosphatase (dUTPase) enzyme is an essential enzyme that protects DNA against uracil incorporation. No organism can tolerate the absence of this activity. In this article, we show that dUTPase function is conserved between E. coli (Escherichia coli), yeast (Saccharomyces cerevisiae) and Arabidopsis (Arabidopsis thaliana) and that it is essential in Arabidopsis as in both micro-organisms. Using a RNA interference strategy, plant lines were generated with a diminished dUTPase activity as compared to the wild-type. These plants are sensitive to 5-fluoro-uracil. As an indication of DNA damage, inactivation of dUTPase results in the induction of AtRAD51 and AtPARP2, which are involved in DNA repair. Nevertheless, RNAi/DUT1 constructs are compatible with a rad51 mutation. Using a TUNEL assay, DNA damage was observed in the RNAi/DUT1 plants. Finally, plants carrying a homologous recombination (HR) exclusive substrate transformed with the RNAi/DUT1 construct exhibit a seven times increase in homologous recombination events. Increased HR was only detected in the plants that were the most sensitive to 5-fluoro-uracils, thus establishing a link between uracil incorporation in the genomic DNA and HR. Our results show for the first time that genetic instability provoked by the presence of uracils in the DNA is poorly tolerated and that this base misincorporation globally stimulates HR in plants

Rapid climate change: scientific challenges and the new NERC programme

In this paper the scientific challenges of observing, modelling, understanding and predicting rapid changes in climate are discussed, with a specific focus on the role of the Atlantic thermohaline circulation. The palaeo and present-day observational and modelling studies being carried out to meet these challenges, under the aegis of a new NERC Rapid Climate Change thematic programme (RAPID), are outlined. In particular, the paper describes the work being done to monitor changes in the meridional overturning circulation of the North Atlantic. The paper concludes with some speculative comments about potential mechanisms for rapid changes